Master Cylinder/Power Booster; Combination Valve - Jeep Cherokee 1999 Electronic Service Manual

X J
DI AGN OSI S AN D T EST I N G (Cont inue d)
a n ABS m a lfu n ct ion h a s occu r r ed. Th e ABS la m p
oper a t es in depen den t ly of t h e r ed wa r n in g la m p.
F or a ddit ion a l in for m a t ion r efer t o Gr ou p 8W.

MASTER CYLINDER/POWER BOOSTER

(1) St a r t en gin e a n d ch eck boost er va cu u m h ose
con n ect ion s. A h issin g n oise in dica t es va cu u m lea k.
Cor r ect a n y va cu u m lea k befor e pr oceedin g.
(2) St op en gin e a n d sh ift t r a n sm ission in t o Neu -
t r a l.
(3) P u m p br a ke peda l u n t il a ll va cu u m r eser ve in
boost er is deplet ed.
(4) P r ess a n d h old br a ke peda l u n der ligh t foot
pr essu r e. Th e peda l sh ou ld h old fir m , if t h e peda l
fa lls a wa y m a st er cylin der is fa u lt y (in t er n a l lea k-
a ge).
(5) St a r t en gin e a n d n ot e peda l a ct ion it sh ou ld
fa ll a wa y sligh t ly u n der ligh t foot pr essu r e t h en h old
fir m . If n o peda l a ct ion is discer n ible, power boost er,
va cu u m su pply, or va cu u m ch eck va lve is fa u lt y. P r o-
ceed t o t h e P OWE R BOOSTE R VACUUM TE ST.
(6) If t h e P OWE R BOOSTE R VACUUM TE ST
pa sses, r ebu ild boost er va cu u m r eser ve a s follows:
Relea se br a ke peda l. In cr ea se en gin e speed t o 1500
r pm , close t h e t h r ot t le a n d im m edia t ely st op t u r n off
ign it ion t o st op en gin e.
(7) Wa it a m in im u m of 90 secon ds a n d t r y br a ke
a ct ion a ga in . Boost er sh ou ld pr ovide t wo or m or e va c-
u u m a ssist ed peda l a pplica t ion s. If va cu u m a ssist is
n ot pr ovided, boost er is fa u lt y.
POWER BOOSTER VACUUM TEST
(1) Con n ect va cu u m ga u ge t o boost er ch eck va lve
wit h sh or t len gt h of h ose a n d T-fit t in g (F ig. 7).
(2) St a r t a n d r u n en gin e a t cu r b idle speed for on e
m in u t e.
(3) Obser ve t h e va cu u m su pply. If va cu u m su pply
is n ot a dequ a t e, r epa ir va cu u m su pply.
(4) Cla m p h ose sh u t bet ween va cu u m sou r ce a n d
ch eck va lve.
(5) St op en gin e a n d obser ve va cu u m ga u ge.
(6) If va cu u m dr ops m or e t h a n on e in ch H G (33
m illiba r s) wit h in 15 secon ds, boost er dia ph r a gm or
ch eck va lve is fa u lt y.
POWER BOOSTER CHECK VALVE TEST
(1) Discon n ect va cu u m h ose fr om ch eck va lve.
(2) Rem ove ch eck va lve a n d va lve sea l fr om
boost er.
(3) Use a h a n d oper a t ed va cu u m pu m p for t est .
(4) Apply 15-20 in ch es va cu u m a t la r ge en d of
ch eck va lve (F ig. 8).
(5) Va cu u m sh ou ld h old st ea dy. If ga u ge on pu m p
in dica t es va cu u m loss, ch eck va lve is fa u lt y a n d
sh ou ld be r epla ced.
Fig. 7 Typical Booster Vacuum Test Connections
Fig. 8 Vacuum Check Valve And Seal
COMBINA TION VALVE
PRESSURE DIFFERENTIAL SWITCH
(1) H a ve h elper sit in dr iver s sea t t o a pply br a ke
peda l a n d obser ve r ed br a ke wa r n in g ligh t .
(2) Ra ise veh icle on h oist .
(3) Con n ect bleed h ose t o a r ea r wh eel cylin der
a n d im m er se h ose en d in con t a in er pa r t ia lly filled
wit h br a ke flu id.
(4) H a ve h elper pr ess a n d h old br a ke peda l t o floor
a n d obser ve wa r n in g ligh t .
(a ) If wa r n in g ligh t illu m in a t es, swit ch is oper a t -
in g cor r ect ly.
(b) If ligh t fa ils t o illu m in a t e, ch eck cir cu it fu se,
bu lb, a n d wir in g. Th e pa r kin g br a ke swit ch ca n be
u sed t o a id in iden t ifyin g wh et h er or n ot t h e br a ke
BRAKES 5 - 9